(1) Field of the Invention
The present invention relates to a method of forming printed images, and particularly to the method of forming printed images in which a photo-sensitive resist film formed on a surface of a copper-clad laminated plate for use in a printed circuit (hereinafter referred to as a copper-clad laminated plate) is colored with a dye.
(2) Description of the Prior Art
The printed-circuit board has conventionally been prepared for a long period of time by a process which comprises forming a photo-sensitive resist film on the surface of a copper foil of the copper-clad laminated plate, exposing the resist film to light through a desired pattern mask, followed by applying a developing treatment to obtain a resist film pattern, and applying etching onto the surface of an exposed copper foil to obtain a desired circuit pattern.
The conventional method of forming the photo-sensitive resist film on the copper foil on the surface of the copper-clad laminated plate includes a method of coating a liquid resist material by use of the conventional coating process such as dipping, roller coating, centrifugal coating and the like, a method of laminating a film-shaped photo-sensitive film called the dry film, for example, Riston film marketed by Du Pont de Nemours & Co. by use of the exclusive sticker, and the like. Recently, however, in place of the above conventional methods, there has been proposed a method of forming the photo-sensitive resist film which comprises coating a photo-curable electrodeposition coating composition.
The method of forming the photo-sensitive resist film by coating the photo-curable electrodeposition coating composition on the copper foil on the surface of the copper-clad laminated plate has such advantages as to be capable of uniformly coating without loss of the starting material and of being incorporated into an automatic line.
However, the aforementioned method raises such a problem that in the case where the photo-sensitive electrodeposition resist film obtained by the aforementioned method has been subjected to exposure to light and to development, it is difficult to judge whether or not the developed printed image has actually been formed as an intended printed image, because the resist film is usually colorless and transparent.
In order to solve the above problems, it is considered to color the resist film, but coloring the resist film requires to disperse and dissolve a coloring pigment or dye in the coating composition, resulting in that the photo-sensitive film formed by use of such an electrodeposition coating composition may cause troubles such as reduction in permeability to ultraviolet light, occurrence of seeds due to deposition of the pigment or dye, gelation of the electrodeposition coating composition due to reaction between the resin and the pigment or dye, disintegration of the emulsion, abnormality of deposition of the electrodeposition coating film, and the like.